/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlineFriendsInterface.h
the stringified version of the enum passed in
namespace EFriendsLists { const TCHAR * EFriendsLists::ToString ( [EFriendsLists::Type](API\Plugins\OnlineSubsystem\Interfaces\EFriendsLists__Type) EnumVal ) }